The present invention concerns a blow device for weft threads in weaving machines. In particular, it concerns a blow device which makes use of a nozzle of the type which consists of a housing, a thread guide duct stretching out through the housing, and blowing means working with the thread guide duct to transport the weft thread. By blowing means are primarily meant the main nozzles of an airjet weaving machine. The invention can also be used, however, for auxiliary main nozzles.
It is known that the main nozzles of airjet weaving machines are provided with compressed air via valves which are controlled by means of a control unit and which are opened at particular moments in the weaving cycle, in particular during the insertion of the weft threads. In the intermediate periods, a weak air flow is continuously supplied via a throttle valve so that the weft threads can be kept in the main nozzles by their ends. When the weaver has to make a threading, only this weak air flow is produced. Only very little suction force is created in this case, which makes the threading rather difficult.
Another well-known method to thread such a main nozzle is to switch on the main nozzles at full power, for example by means of a push button which transmits a signal to the aforesaid control unit, as a result of which the main nozzle in question operates at full capacity for a certain period. Given the big air flow and the blow direction, the suction force at the entry of the nozzle is also weak in this case. Moreover, this method is disadvantageous in that the thread end which has been sucked up by the strong air flow exerted upon it is entirely unravelled.
The present invention concerns a blow device for weft threads in weaving machines, in particular a blow device which makes use of the aforesaid type of nozzles, which does not have the above-mentioned disadvantages.
To this end, it is made up of a blow device for weft threads in weaving machines, in particular a blow device which makes use of a nozzle of the type which consists of a housing, a thread guide duct stretching out through the housing, and first blowing means situated in the housing and working with the thread guide duct to transport the weft thread to the shed, characterized in that the nozzle has second blowing means, also situated in the housing and working with the thread guide duct, to thread the nozzle, whose second blowing means are made up of at least one blow duct which ends at an angle in the thread guide duct, which makes it possible to thrust a weft thread presented at the entry of the thread guide duct through the thread guide duct.
These second blowing means preferably have exactly one blow duct which ends at an angle in the thread guide duct and whose section and said angle are selected such that, on the one hand, the thrust force is sufficiently strong for the threading, but on the other hand not sufficiently strong to unravel the weft thread.
The blow device according to the invention is also provided with means which allow the second blowing means to be easily switched on and off.
According to a preferred embodiment, these means consist of a compressed air junction provided with a manually operated valve which has been built into the housing of the nozzle, such that a very compact construction is obtained.
According to a variant, use is made of an electromagnetic valve operated by means of a push button, such that when it is energized, said valve is opened and the above-mentioned second blowing means are activated, and such that, also by means of appropriate valves, the air supply to the first blowing means which transport the weft thread are closed off completely.